As an aircraft approaches its destination, it needs to descend from its cruising altitude to land at the destination airfield and, in the process, also slow down to the appropriate descent speeds and honor any time constraints imposed by air traffic control (ATC). This implies that, from the top-of-descent point to touchdown, the aircraft needs to lose kinetic and potential energy at the appropriate rate, dissipating it as it flies down the descent path. In the scope of the present invention, the sum of kinetic and potential energy is referred to as the aircraft's energy. Correctly managing energy loss requires adequate planning which, whilst being a routine task for the flight crew, distractions or delay in descent and/or slowing down can result in the aircraft arriving at salient points throughout the descent with inadequate energy levels. Tactical complications such as those involving weather or unplanned traffic constraints may result in ATC requesting a combination of speed and altitude deviations that may preclude the flight crew from executing the planned descent actions. This, of course, interferes with the energy dissipation plan and requires the crews to be vigilant in assessing and taking action to recover any energy upsets in time before approach and landing in such circumstances.
Consequently, inadequate energy management is a major concern in the descent and approach phases of flight to continued safety in flight operations, and has been considered as a potential precursor to unstabilised approaches. When descent energy deviates from an intended profile, corrective recovery actions need to be taken in good time. The task of recovering from an undesirable energy state whilst approaching a terminal area significantly increases the crew workload, particularly when operating into busy airfields in bad weather conditions or high terrain. Even in today's environment where the time-of arrival is not enforced, there is still a need to provide energy management and alerts to the crew, as they do not currently have a reliable means of identifying the solutions that can be adapted. Current practices allow some form of visualization of the target aircraft recapture point along the flight plan, but it is very difficult to get a clear picture of the future situation when alterations to the lateral flight plan will be required.
A number of incidents have occurred where incorrect energy management was cited as one of the main causal factors leading to the event. Indications suggest that energy handling difficulties can sometimes be traced to actions carried out in the descent, sometimes as early as initial descent. Despite the expected safety enhancement associated with the introduction of trajectory based operations (TBO) envisaged by Single European Sky Air Traffic Management Research (SESAR) and Next Generation Air Transportation System (NEXTGEN) for the future air navigation system, disruptions to the intended descent path or actions will remain. These disruptions may be due to unexpected conditions associated with weather, traffic, runway closures, aircraft malfunctions, inappropriate aircraft control or other unaccounted operational scenarios. As a result, situations will continue to occur where an aircraft diverges from the intended energy profile.
With the introduction of continuous descent approach (CDA) procedures, these deviations are becoming more difficult to recover. This is due to steeper profiles, that enable a continuous descent at idle thrust with minimal level segments associated with today's step-down descents. The aircraft will therefore have more energy than those flying current day procedures and therefore smaller deviations will be required before the aircraft energy is unrecoverable within the remaining track distance to the runway, requiring air traffic control (ATC) intervention.
some conventional systems in current generation aircraft already provide an indication relating to the lateral and vertical deviations from the flight plan. This information, together with the descent speed, can be used by the flight crew to assess the aircraft's energy state and determine whether any corrections are required to adjust the total energy (which can be achieved by adjusting engine thrust, speed or drag) or the distribution between the kinetic and potential energy (by trading off speed for altitude). A further possible adjustment is changing the lateral path to vary the remaining track miles to be flown, thus increasing the distance over which the excess energy can be dissipated. However, conventional systems do not provide any advice to the crew in selecting the appropriate actions when energy adjustments are required. Such advice is particularly desirable when time-of-arrival constraints are also imposed, as any deviations from the original descent plan would introduce variations in the time-of-arrival instant. For instance, an aircraft would arrive late if track miles were added to the flight plan (to increase the energy dissipation distance) without adjusting the descent speed. The required automation, therefore, needs to take into consideration both the energy and time constraints imposed on the descent path such that any energy recovery adjustments do not, if possible, disrupt the intended time of arrival at salient waypoints. Accordingly, it is desirable to provide an improved aircraft system that is capable of determining the required adjustments to recapture the aircraft's energy whilst honoring speed, altitude and time constraints at salient points along the descent trajectory.